In hip replacement surgery, the natural head and neck portion of the femur are removed and replaced with a metallic hip prosthesis. This prosthesis generally comprises three elements: a distal stem portion for fixation into the distal part of the femur, a proximal body portion for fixation in the metaphysis of the femur, and a neck portion for replacing the natural femoral neck. These elements can be connected and configured in numerous ways, but generally these elements form either a one-piece prosthetic hip design or a modular prosthetic hip design.
One-piece designs are typically formed from a solid piece of metal, such as titanium, stainless steel, or cobalt chromium alloys. As such, the stem, proximal body, and neck are integrally formed together. Even though the implants are manufactured in a wide range of shapes and sizes, the individual elements cannot be separately altered or sized since no changes or adjustments occur between the elements themselves.
In contrast to one-piece designs, modular designs have some components that are interchangeable. Specifically, modular hip prostheses are formed from individual, separate components that are interchangeable and connectable together. The amount of modularity and degree of adjustability between components varies widely depending on the design and manufacturer of the prosthesis.
Some prior modular designs offer limited modularity between the individual, separate components. U.S. Pat. No. 4,846,839 entitled “Apparatus for Affixing a Prosthesis to Bone” to Noiles teaches, in one embodiment, a proximal body that connects to a stem and neck integrally formed together. Here, the neck has no adjustability since it is permanently affixed to the stem. Further, the proximal body locks to the stem in a single location.
U.S. Pat. No. 5,002,578 entitled “Modular Hip Prosthesis Apparatus and Method” to Lumen teaches, in one embodiment, a femoral neck that connects to a stem and proximal body integrally formed together. The neck is rotationally adjustable about an end of the stem, but the stem and proximal body are not adjustable. In another embodiment, the proximal body attaches to the proximal end of the stem. Here, the proximal body and neck are rotationally adjustable but the proximal body is not axially adjustable along the stem.
U.S. Pat. No. 5,702,480 entitled “Modular Hip Joint Prosthesis” to Kropf et al. teaches a modular prosthesis including a stem, a cervical part, a screw, a coupling member, and a metaphysary. The metaphysary abuts against a shoulder on the outer surface of the stem while the coupling member connects the cervical part to the metaphysary. The metaphysary has no axial adjustability along the stem.
U.S. Pat. No. 5,725,592 entitled “Modular Prosthesis Having Neck Component Connected to Stem Component Through Cavity in Body Component” and U.S. Pat. No. 5,902,340 entitled “Method of Assembling a Modular Prosthesis Used for Bone Replacement” to White, Hayes, et al. teach multiple embodiments that use multiple interlocking taper connections to connect a stem, proximal body, and neck. In several embodiments, the proximal body includes two tapered sections that taper lock to both the neck and stem. In another embodiment, the proximal body has an internally tapered bore that taper locks to a tapered section on the outer surface of the stem.
U.S. Pat. Nos. 5,876,459 and 5,906,644 entitled “Adjustable Modular Orthopedic Implant” to Powell teach multiple embodiments directed to a femoral hip stem. In one embodiment, the proximal body is integrally formed to the stem, and the neck is positioned in a bore in the end of the stem to rotate about the stem. In another embodiment, the proximal body affixes to a proximal end of the stem that has a tapered section to receive the proximal body. The neck includes a split collet that fits into a bore in the proximal body. In yet another embodiment, the proximal end of the stem has an integrally formed split collet. The proximal body fits over the collet while the neck has an elongated threaded section that threads into a bore that extends into the end of the stem.
U.S. Pat. No. 6,139,584 entitled “Proximal Femoral Sleeve for a Revision Hip Prosthesis” to Ochoa et al. teaches a proximal body with a tapered bore for taper locking with a tapered section of the stem. The proximal body has an eccentric outer surface portion with a symmetrical region and a compensating region for offsetting bone loss or other anatomical anomalies. This proximal body is not axially adjustable along the stem.
U.S. Pat. No. 6,299,648 entitled “Locking Hip Prosthesis” to Doubler and Hammill teaches a stem with a proximal portion that is telescoped into one end of a bore in the trochanter element. The mating surfaces of the shaped rod and the trochanter bore form a rotationally immovable connection. A neck element is telescoped into the other end of the trochanter bore permitting rotational adjustment. All the elements are locked together with a bolt through the neck and stem.
U.S. Pat. No. 6,319,286 entitled “Modular Hip Prosthesis” to Fernandez et al. teaches a proximal body with a bore having two sections. A first section of the bore receives a proximal end of the stem, and a second section of the bore receives a distal portion of the neck.
Other hip designs offer different modularity between the various components. Some designs, for example, use an integrally formed stem and proximal body that are connectable to a removeable neck. In these designs, the neck is modular only with respect to the stem and proximal body component. Some prior modular designs also offer limited adjustability between the individual, separate components.
Prior hip prostheses, then, do not offer sufficient adjustability and modularity between the stem, proximal body, and neck. This lack of adjustability and modularity limit the ability of the hip prosthesis to match various anatomical conditions encountered during a femoral surgical procedure. Specifically, the neck, proximal body, and stem should offer sufficient variability to meet physiologically different sizes, shapes, and proportions. A hip prosthesis with such variability would offer significant advantages over prior prostheses.
It therefore would be advantageous to provide an implantable orthopedic hip prosthesis that offered a wide range of adjustability and modularity between the stem, proximal body, and neck.